The present invention generally relates to an automatic implantable atrial defibrillator, system, and method for delivering cardioverting or defibrillating electrical energy to the atria of a human heart and which is capable of providing the cardiologist with important information related to the condition of the patient and the interaction between the implanted defibrillator and the patient's heart. More particularly, the atrial defibrillator of the present invention is capable of transmitting, for simultaneous display on an external programer display, multiple internally generated electrograms, one or more internally generated electrograms with event detection criteria and/or event detection indicia, or multiple internally generated electrograms together with indicia showing when cardioverting energy delivery criteria are satisfied by the patient's heart activity.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. Patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly and many times can only be corrected by external defibrillation of the type well known in the art. This treatment involves applying a relatively large quantity of electrical energy to the heart with external skin surface electrodes. The energy is applied in synchronism with a detected R wave (electrical activation) of the heart. The treatment is very painful and can necessitate hospitalization for as many as a few days. Unfortunately, most often, it only provides temporary relief, lasting but a few weeks.
Drugs are available for reducing the incidents of atrial fibrillation. However, such drugs have many side effects. Also, many patients are resistant to them which greatly reduces their therapeutic effect.
In order to negate the need for external defibrillation and drug therapy, implantable atrial defibrillators have been proposed to provide relief for patients suffering from occurrences of atrial fibrillation. Two such defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting or defibrillating the heart. Both of these defibrillators required the patient to recognize the symptoms of atrial fibrillation. One defibrillator required a visit to a physician for activating the defibrillator. The other defibrillator required the patient to activate the defibrillator with a magnet from external to the patient's skin.
It is preferable that an implantable cardiac device, such as an atrial defibrillator, be truly automatic. In order for an implantable atrial defibrillator to be truly automatic, it must be able to accurately detect atrial fibrillation and then safely apply electrical energy to the atria to convert the same to normal sinus rhythm (NSR).
Detection of atrial fibrillation is a two-part process. First, an atrial defibrillator must be able to sense activity of the heart, such as atrial activity. One atrial defibrillator having such capability is fully disclosed in Jin et al., U.S. Pat. No. 5,267,559 which issued on Dec. 7, 1993 for ATRIAL DEFIBRILLATOR AND METHOD FOR PROVIDING ATRIAL SENSING and which is assigned to the assignee of the present invention and incorporated herein by reference.
After heart activity, such as atrial activity, is sensed, an atrial fibrillation detector then must determine if the sensed heart activity satisfies a fibrillation criteria. One such detector is fully disclosed in co-pending U.S. application Ser. No. 08/233,251, now U.S. Pat. No. 5,522,852, filed Apr. 26, 1994 in the names of Harley G. White and Joseph M. Bocek for SELECTIVE CARDIAC ACTIVITY ANALYSIS ATRIAL FIBRILLATION DETECTION SYSTEM AND METHOD AND ATRIAL DEFIBRILLATOR UTILIZING SAME. Another such detector is fully disclosed in co-pending U.S. application Ser. No. 08/278,055, now U.S. Pat. No. 5,486,199, filed Jul. 20, 1994 in the names of Jaeho Kim and Harley G. White for SYSTEM AND METHOD FOR REDUCING FALSE POSITIVES IN ATRIAL FIBRILLATION DETECTION. Both of the aforementioned co-pending applications are assigned to the assignee of the present invention and incorporated herein by reference.
Each of the aforementioned co-pending applications discloses a preferred embodiment of an atrial fibrillation detector wherein atrial cardiac events are detected from sensed atrial activity. Further, each of these preferred embodiments includes ventricular activity sensing and the detection of R waves from the sensed ventricular activity.
Once atrial fibrillation is detected, it is then preferred to apply cardioverting electrical energy to the atria to return the heart to NSR. To assure that the cardioverting electrical energy is safely applied to the atria, it is preferred that the energy be applied in synchronism with a detected R wave. To that end, co-pending U.S. application Ser. No. 08/259,476 filed Jun. 14, 1994 in the name of Harley G. White for CARDIOVERSION SYNCHRONIZATION SYSTEM AND METHOD FOR AN ATRIAL DEFIBRILLATOR, which is assigned to the assignee of the present invention and incorporated herein by reference discloses a synchronization system which includes two ventricular sense channels and requires that an R wave be sensed in both channels before the energy may be applied. In addition, other synchronization criteria may be required to be satisfied such as a minimum interval criteria as described, for example, in Adams, et al., U.S. Pat. No. 5,207,219, which issued on May 4, 1993 for ATRIAL DEFIBRILLATOR AND METHOD FOR PROVIDING INTERVAL TIMING PRIOR TO CARDIOVERSION, and which is assigned to the assignee of the present invention and incorporated herein by reference.
Hence, as can be seen from the foregoing, an automatic atrial defibrillator must reliably sense heart activity, reliably detect cardiac events, and apply energy delivery criteria to sensed heart activity. In order to assure that the defibrillator will perform the above functions at the time of implant and thereafter, it would be desirable for the defibrillator to have the capability to provide the cardiologist with adequate information to verify that it is functioning appropriately. For example, in addition to cardiac event detection indicia, it would also be desirable to provide the cardiologist with information relating to cardiac event detection criteria, such as detection thresholds, and, where heart activity criteria must be met for cardioverting energy to be applied, indicia when such criteria are met would also be helpful. In the latter case, such indicia could facilitate parameter adjustment from default perimeter values to render successful therapy possible where such successful therapy may otherwise be unobtainable.
It would also be desirable for the cardiologist to be provided with more then one electrogram where more then one sense channel is used to determine the condition of the heart. This is especially important where more then one sense channel is required to provide therapy intervention.